Crystal separating process



separation. A modification United States Patent 2,992,141 CRYSTALSEPARATING PROCESS David D. Peebles, Davis, Califi, assignor to ForemostDairies, Inc., San Francisco, Calif., a corporation of New York FiledJune 2, 1958, Ser. No. 739,309 17 Claims. (Cl. 127-61) This inventionrelates generally to processes and apparatus for removing solids fromfluid mixtures. Particularly it has been applied to the removal oflactose from liquid whey.

Liquid whey, such as is produced as a by-product in the manufacture ofcheese, has a lactose content of the order of 67% (dry solids basis). Anumber of commercial processes have been used for the manufacture oflactose from such raw material. In one such process a portion of theprotein of the whey is coagulated by addition of lime and application ofheat, after which the coagulated solids together with precipitatedcalcium phosphate and other insoluble solids, are removed bydecantation, filtration, or centrifugation. efiiuent is thenconcentrated by evaporation, and lactose is crystallized from theconcentrate. The crystallized lactose is then removed from the motherliquor as by centrifuging, and further purified as by washing, byresolution and recrystallization, or both. It will be apparent that sucha process seriously impairs or destroys the protein constituents of thewhey solids. Furthermore, a substantial amount of solids from the wheyare associated with the removed lactose crystals, thus requiringextensive washing or other treatment for purification. Anothercommercial process (see Patent 2,439,612) involves concentrating liquidwhey by vacuum evaporation together with heat treatment, after whichlactose is crystallized from the concentrate. Lactose crystals areremoved from the material as by centrifuging or hydraulic of the lastdescribed process -(see Patent 2,768,912) involves treatment of thecrystallized concentratein a rotating screen equipment, for

removing the lactose crystals. The lactose crystals must The clarifiedbe relatively large for effective removal. Both of the last describedprocesses, in contrast with the subject invention, involve removal ofthe lactose crystals with substantial amounts of other solids of thewhey, thus complicating subsequent purification procedures.

In general, it is an object provide a process utilizing a novelprocedure for the removal of lactose crystals from a liquid medium.

Another object of the invention is to provide a process which is moreeconomical than prior processes, and which provides an effluent that canbe spray dried to form a powdered product.

Another object of the invention is to provide a process capable of.continuous operation for the removal of lactose crystals.

Another object of the invention is to provide a process of the abovecharacter which removes the lactose crystals together with only arelatively small amount of other whey solids, thus simplifyingsubsequent washing or other purification procedures.

of the present invention to view in side elevation illus- Patented July11, 1961 trating essential parts of the apparatus and the manner inwhich the process is carried out.

FIGURE 2 is a side elevational view in section illustrating a morecomplete apparatus for carrying out the present process.

FIGURE 3 is a flow sheet illustrating the process.

Referring particularly to the removal of lactose from whey, the presentinvention involves producing a whey concentrate containing a substantialamount of crystalline lactose in the form of discrete solids. Inpractice, the lactose crystals can be formed by first concentrating rawliquid whey, as by vacuum evaporation, to produce a concentratesupersaturated with respect to its lactose content, and then subjectingsuch concentrate to controlled crystallization to produce lactosecrystals of a size suitable for the present process. This mixture isthen subjected to atomization, with the material resulting fromatomization being discharged through a treatment zone. The materialpassing through the treatment zone consists of liquid droplets andlactose crystals forming the solid fraction, with both the droplets andthe solids moving at relatively high speeds in free flight. Separatingforces are applied to the material moving through the treatment zone,whereby separation and orientation takes place between the crystalsolids and the liquid droplets. The separated fractions are thencollected from the regions into which they are discharged.

The apparatus schematically illustrated in FIGURE 1 consists of -acentrifugal atomizer head 10. This device can be similar to devicescommonly used in the milk industry in connection with spray dryingequipment. A feed line 11 is shown for introducing material into theatomizer. Conduit means is provided for delivering a current of air orother gas toward one side of the annular region surrounding theatomizer. This conduit means can consist of the concentric conduits 13,14 and 15, which form between them the annular passages 16 and 17. Theinner conduit 15 also forms a passage 18 terminating immediately abovethe head. On the other side of the atomizer head, the conduit or shell21 forms a passage 22 which is alined with and generally opposed to thepassages 16 and 17 In FIGURE 2, the parts illustrated schematically inFIGURE 1, are incorporated in more complete equipment. The conduit means12 and 21 are disposed within the chamber 23, which has a lower conicalportion in communication with the exhaust conduit 24. Conduit means 12extends through the top wall 26 of the chamber 23, whereby the passages16 and 17 communicate with the chamber 27. Gas is delivered to chamber27 and thus to the passages 16 and 17, by way of conduits 28. Anotherchamber 29 communicates with the upper end of passage 18, and connectswith conduit 31 whereby air or other gas is supplied to a region closelyadjacent one side of the atomizer head, as shown in FIGURE 1. The innerconduit means 21 connects with the external conduit 32. A manifold 33 isshown surrounding the chamber 23, and is connected with chamber openings34. for introduction of air or other gas.

The atomizer head 10 should be capable of producing relatively uniformatomization of viscous concentrates. Good results in the separation oflactose have been obtained by using a head of the circumferentiallyspaced impact bar type wherein bars are disposed in circumferentiallyspaced arrangement at the outer periphery of a hollow rotating head.Atomizer heads of this type are disclosed .in Patent 1,939,364.

Typical use of the apparatus shown in FIGURE 2 involves connectingconduit 32 with the suction side of a blower, through a separator of thecyclone type. Conduit 24 can likewise be connected to the suctionside'of a blower, through a separating cyclone. A controlled amount ofair is admitted through the conduits 28 to flow downwardly throughpassages 16 and 17. A limited amount of air is introduced by way ofconduit 13 and passage 18, to minimize back swirl of the atomizedmaterial inwardly over the atomizer head. A controlled amountof air isshown being introduced through the openings 34 to cause swirlingmovement of air within the chamber 23, with this air progressinginwardly and ultimately downwardly through the conduit 24. Use of thisfeature tends to increase the efficiency of crystal separation.

As previously stated, the invention has been used successfully for theseparation of alpha monohydrate lactose crystals from a wheyconcentrate. Such a mixture can be prepared by subjecting a suitable rawliquid whey to vacuum evaporation to produce a concentrate which, forexample, may range from 40 to 55% solids. At normal temperatures, suchconcentrates are supersaturated with respect to their lactose content.Lactose can be crystallized from such a concentrate by known methods,involving for example seeding of the concentrate with lactose crystalstogether with gradual cooling and agitation over an extended period. Intypical instances from 50 to 75% of the lactose content may becrystallized, with the major portion of the crystal particles rangingfrom about 105 to 840 microns in size. Assuming that such a wheyconcentrate is supplied to the atomizer head 10, centrifugal atomizationtakes place with discharge of material outwardly from the periphery ofthe rotating head in a generally planar annular zone. In FIGURE 1 thiszone is indicated at 36. Gas discharging from the passages 16 and 17forms a relatively non-turbulent stream directed toward one side of thezone 36, and in this manner separating forces are applied. Withouttheorizing upon the exact manner in which separation takes place, thenet result is to cause deflection and orientation of liquid dropletsdownwardly, while the lactose solids become disengaged from the liquiddroplets and continue outwardly on a more elevated trajectory. In FIGURE1, the region 37 is occupied substantially entirely by lacrtosecrystals, while the region 38 overlying the open end of the conduit 21is occupied by atomized liquid droplets. Between these two regions,there is a transitional region, which however is relatively sharplydefined. The downward current of gas through the conduit 21 plays a partin deflecting the material being discharged from the atomizer, and theprocess is carried out in such a manner that substantially all of theatomized liquid droplets are drawn downwardly into the conduit 21,whereby the lactose crystals proceed beyond the conduit 21, and into thelower portion of the chamber 23, for withdrawal through the conduit 24.Air introduced through openings 34 swirls about the chamber 23 and alsoenters conduit 21 over its upper edge. This serves to increase thesharpness and efiiciency of separation.

It is a relatively simple matter to adjust the process and apparatus toobtain the desired separation. Thus water can be supplied to theatomizer head, and the rate of flow through the passages 16 and 17 andthe conduit 21 adjusted whereby practically all of the liquid dropletsare drawn into the conduit 21 instead of being discharged into thechamber 23. The region occupied by the liquid droplets, adjacent theopen end of the conduit 21, should be of a diameter only slightly lessthan the internal conduit diameter. Small amounts of air are admittedthrough conduit 18 to prevent back swirl. Substantial amounts of air, asfor example about one-half of the total air supplied, is introducedthrough openings 34. If now the concentrate containing the lactosecrystals is supplied to the atomizer, separation takes place aspreviously described, with substantially all of the liquid dropletsbeing drawn into the conduit 21.

Lactose in solution, and the smaller lactose crystals (e.g. less thanabout 105 microns) remain with the liquid droplets. In general, theseparated lactose maycomprise 4 from 40 to 70% of the total lactose ofthe whey, and from 70 to or more of the crystallized lactose.

In some instances it is desirable to use the process primarily for thepurpose of separating lactose crystals from the mother liquor. In suchevent, air or other gas at room temperatures can be supplied to theequipment. I have discovered, however, that further concentration orspray drying can be carried out simultaneously with the separatingoperation. Thus assuming that it isdesired to remove a portion of themoisture contained in the liquid separated fraction, the air supplied byway of conduits 28 and 33 is heated, whereby the liquid droplets aredispersed in drying air, thus removing moisture by evaporation. Bycontrolling the inlet and outlet temperatures of the drying air, theamount of evaporation can be controlled as desired, whereby the materialdelivered toconduit 21 is either a concentrate, or a dry powderedmaterial.

Irrespective of Whether the evaporation of the liquid fraction takesplace simultaneously with crystal separation, the material collected andremoved through conduit 24 has very little moisture content, and isrelatively free of impurities. Assuming the separation of lactose in themanner previously described with air at room temperature, the freemoisture content of the separated lactose may be reduced to belowapproximately 10%, and the residual whey solids (other than lactose) maycontain from 35 to 50% solids. By relatively simple secondary drying,the free moisture content of the lactose fraction can be reduced to avalue of approximately 3% or less. Such secondary drying can be carriedout for example by passing the material through one or more cyclonessupplied with hot air. Also some secondary drying can be carried out byelevating the temperature of the air introduced through openings 34. Therelatively low percentage of impurities with the lactose crystals makesit possible to use such a product for many purposes, without furtherprocessing. However, it can be readily processed by known methods, asfor example by washing, dissolution and reprecipitation, or both, toproduce a lactose of the desired purity.

The flow sheet of FIGURE 3 illustrates a continuous process for theremoval of a crystal solid-like lactose. In this instance a mixture ofliquid and crystal solids, such as a whey concentrate containing alphalactose monohydrate crystals, is supplied to the separating operation 1,carried out in the manner previously described. The atomized liquidfraction is shown either being collected as a liquid at 2, beingsubjected to drying at 3 to produce a spray dried powder, or to partialevaporation at 4 to produce a liquid concentrate. Some such liquidconcentrate may be recycled as indicated.

Examples of my process are as follows:

Example I An edible grade of raw liquid whey was concentrated by vacuumevaporation to produce a concentrate containing 55% solids. Thisconcentrate was removed from the last evaporating stage at a temperatureof 140 F. The concentrate was seeded with lactose crystals and graduallycooled over a period of about 48 hours with gentle agitation.Substantially 70% of the lactose content crystallized as alpha lactosemonohydrate, and the bulk of the crystals were of a size ranging from to840 microns. This concentrate was fed to apparatus as described inconnection with FIGURES 1 and 2, with air being supplied at normal roomtemperature. Both conduits 13 and 21 had internal diameters of about 36inches. The centrifugal atomizer head had an external diameter of 10inches and circumferentially spaced impact bars. It was located about 12inches from conduit 21. The atomizer head and the speed of rotation(about 1500 r.p.m.), were such that if used as an ordinary spray drierfor producing spray dried skim milk solids, the dried particles wouldhave a size of the order of about 50 microns. Air was exhausted throughconduit 12 at a velocity of about 15 Percent Alpha lactose monohydrate96 Other solids 3 Free moisture 1 The separated lactose fraction was afree-flowing material. Of the total amount of lactose in theconcentrate, 65% was separated out and delivered to conduit 24. Withrespect to the lactose contained in the collected liquid droplets about95% of the same was in the form of lactose crystals smaller than about105 microns.

Example 2 The process was carried out in the same manner describedabove, but hot air at a temperature of about 320 F. was admitted to theconduits 28 and 33, and the rate of feed of the concentrate was reducedto produce an air outlet temperature through conduit 32 of about 180 F.Under such conditions, the liquid fraction was dried to form a drypowdered edible product, similar to ordinary commercial spray driedwhey, except for its lactose content.

While the invention has been described as employed for the separation oflactose crystals from a whey concentrate, it is deemed to be applicableto separating operations on other material having comparablecharacteristics.

In the foregoing explanation, reference is made to the application ofseparating forces by virtue of the relatively non-turbulent current ofair delivered through conduit passages 16 and 17 and directed towardzone 36. The current of air applies separating forces because itdeflects the liquid droplets to an extent greater than deflection of thecrystal solids. In addition to separating forces created by virtue ofthe air current, it is deemed probable that other forces exist tendingto cause effective seperation. For example, it is probable that thenon-spherical crystal solids are discharged with considerable rotationor spin about their individual axes, which tends to free them fromliquid. In addition, any liquid droplets containing or incorporatingcrystal solids of substantial size tend, by virtue of the presence of acrystal, to subdivide and thus free the liquid from the crystal. Thisfreeing action may be aided by surface and interfacial tension effects.During the separating operation a crystal may be reduced in size bybreakage, depending upon such factors as crystal size and hardness andthe speed of rotation of the atomizer head. Whether all or only some ofthe above described factors are responsible, separation in accordancewith my process is remarkably efiective, and makes possible relativelyhigh capacity continuous sep arating operations.

In general, the present process provides a simple procedure for thecontinuous removal of crystal solids. The process is more economicalthan prior processes, and is flexible in that it can be adapted to awide variety of requirements and conditions.

I claim:

1. In a separating process for the treatment of a hydrous fluid mixturecontaining discrete solid particles and liquid fractions, the steps ofsubjecting the mixture to centrifugal atomization whereby droplets ofthe liquid fraction and the discrete solid particles are dischargedoutwardly through an annular treatment zone surrounding the region ofatomization, the discrete solid particles containing less than aboutfree moisture, subjecting the material while in flight through said zoneto a flow of gas to apply additional separating forces to thereby effecta substantial separation of the droplets from the discrete solidparticles, and then. separately collecting the fractions leaving saidzone, one fraction being a non-fluid mass comprising mainly the discretesolid particles.

2. A process as in claim 1 in which the additional separating forces areapplied by subjecting the material in said separating zone to a streamof gas directed generally at right angles to the direction of flight ofmaterial in said zone.

3. In a separating process for the treatment of a hydrous fluid mixturecontaining a liquid fraction and lactose crystals, atomizing the mixtureand discharing the resulting material through a zone of separation, thedischarging material comprising liquid droplets and discrete lactosecrystals containing less than about 10% free moisture, subjecting thematerial while in said zone to a flow of gas to apply separating forces,and then collecting the separated discrete lactose crystals leaving saidzone.

4. A process as in claim 3 in which said zone is annular and generallyplanar.

5. A process as in claim 3 in which a current of gas is directed towardand through said zone from one side thereof to thereby apply separatingforces.

6. In a process for the removal of lactose from an aqueous liquidlacteal material containing the same, the steps of forming a concentrateof the material with a portion of its lactose in a condition ofsupersaturation, crystallizing lactose in the concentrate to providecrystal particles ranging generally from about to 840 microns in size,subjecting the concentrate to atomization whereby atomized droplets andlactose crystals are discharged through a zone adjacent the region ofatomization, directing a stream of gas toward and through said zone fromone side thereof to thereby cause separation between solid lactosecrystals and liquid droplets, the separated lactose crystals containingless than about 10% free moisture, and then collecting the separatedlactose crystals.

7. A process as in claim 6 in which said stream of gas is hot drying gaswhereby moisture is evaporated from the liquid droplets.

8. A process as in claim 7 in which the hot drying gas effects removalof moisture from the liquid droplets to form a dry powdered material.

9. In a separating process for the treatment of a hydrous fluid mixturecontaining discrete solid and liquid fractions, atomizing the mixture toform atomized droplets of liquid material and discrete solid particlescontaining less than about 10% free moisture, discharging the resultingmaterial in free flight through a zone of separation, subjecting thematerial while in said zone to a flow of gas to apply separating forcesto thereby effect a substantial orientation of liquid droplets relativeto the discrete solids, causing the separated liquid fraction to bedispersed in a hot drying gas whereby moisture is removed from the sameby evaporation, and separately collecting the discrete solids from theother material.

10. A process as in claim 9 in which moisture is removed from the liquiddroplets by evaporation to produce a liquid concentrate.

11. A process as in claim 9 in which moisture is removed from the liquiddroplets while dispersed in said drying gas to produce a dry powderedmaterial.

12. In a process for the treatment of a fluid material containingdiscrete solid and liquid fractions, atomizing the material anddischarging the resulting material in free flight through an annularzone of separation, said zone being generally planar, directing acurrent of hot drying gas toward and through said zone from one sidethereof to thereby apply separating forces to efiect a substantialorientation of liquid droplets relative to the solids and to effectdispersion of the liquid droplets in said gas to thereby remove moisturefrom the same by evaporation, and then collecting the solids separatelyfrom the other material leaving said zone.

13. In a separating process for the treatment of a fluid mixturecontaining lactose crystals and an aqueous liquid fraction,.subjectingthe mixture to atomizing forces where- :by the material is discharged asatomized droplets together with-discrete solid lactose crystalscontaining less than about 10% free moisture, said discharge beingthrough an annular zone that is generally planar, directing a current ofhot drying air toward said zone from one side thereof whereby thelactose crystals and droplets in said zone are subjected to forces tothereby efiect a substantial orientation of the droplets relative to thelactose crystals and whereby moisture is evaporated from the liquiddroplets, collecting the lactose crystals discharging outwardly fromsaid zone, and separately removing material from a region on the other.side ofsaid zone.

14. In a process for the removal of a crystallizable substance from anaqueous liquid material containing the same, the steps of forming aconcentrate of the material with a portion of said substance in acondition of supersaturation, crystallizing solid particles of thesubstance in the concentrate to provide crystal particles ranginggenerally from 105 to 840 -microns in size, subjecting the concentrateto atomization whereby atomized droplets and crystal solids containingless than about 10% free moisture are discharged through a zonesurrounding the region of atomization, directing a current of gas towardand through said zone to effect separation between said crystal solidsand liquid droplets, and collecting the crystal solids separated fromthe remaining material.

l5. Inqa process for the treatment of a fluid mixture containing aliquid fraction and discrete solids, atomizing the mixture anddischanging the resulting material through an annular zone ofseparation, :directing a stream of gas toward and through saidzzone fromone side thereof, withdrawing gas in a region on the other side of saidzone together with atomizedliquid droplets, collecting discreteReferences Cited 'in the file of this patent UNITED STATES PATENTS2,088,606 Peebles et al. Aug. 3, 1937 2,461,584 Anderson Feb. 10, 19492,525,224 Kaiser Oct. 10, 1950 2,555,213 Wallace May 29, 195 1 2,575,119Peebles-et al =Nov. 13, 1951 2,559,989 Nyrup July 10, 1951 2,566,292Reese Aug. 28, 1951 2,768,912 Peebles etal Oct. 30, 1956

6. IN A PROCESS FOR THE REMOVAL OF LACTOSE FROM AN AQUEOUS LIQUIDLACTEAL MATERIAL CONTAINING THE SAME, THE STEPS OF FORMING A CONCENTRATEOF THE MATERIAL WITH A PORTION OF ITS LACTOSE IN A CONDITION OFSUPERSATURATION, CRYSTALLIZING LACTOSE IN THE CONCENTRATE TO PROVIDECRYSTAL PARTICLES RANGING GENERALLY FROM ABOUT 105 TO 840 MICRONS INSIZE, SUBJECTING THE CONCENTRATE TO ATOMIZATION WHEREBY ATOMIZEDDROPLETS AND LACTOSE CRYSTALS ARE DISCHARGED THROUGH A ZONE ADJACENT THEREGION OF ATOMIZATION, DIRECTING A STREAM OF GAS TOWARD AND THROUGH SAIDZONE FROM ONE SIDE THEREOF TO THEREBY CAUSE SEPARATION BETWEEN